Unit dose dispensers, or dispensers having metering valves that discharge predetermined volumes of liquefied formulation art known in the art. Where the formulation includes medication for certain specific purposes, such as medication for use in nasal passages and the like, a metering valve that discharges fixed volumes of each medication at each discharge is desired. Several such valves are disclosed in the following references: U.S. Pat. Nos. 4,892,232; 5,105,995; 5,085,351; 5,183,187; 5,484,088; 6,695,175; and, 6,910,606.
Existing metering valves discharge liquefied formulation from a pressurized container filled either prior to attaching the valve or dispensing apparatus at the upper end of the container, or through a port at the bottom of the container. It is often desirable, however, to fill the formulation through the dispensing valve or apparatus. For example, formulations that include an evaporant, such as needed to create a mist or foam, are retained in a bag within the container, with the bag being surrounded in the container by a propellant. As such, the propellant pressurizes the bag thereby retaining the liquefied formulation or gas in a liquid state.
It should be noted, existing adjustable metering valves are not suitable for discharging a formulation that includes a liquefied gas that is retained in liquid form by the propellant. This is because the liquefied evaporant turns to gas as soon as the valve opens the metering chamber to ambient thereby causing all the formulation in the metering chamber, not just that portion adjacent a movable wall of the metering chamber, to be discharged through the valve. Those unit dose valves that are not adjustable, however, can discharge a fixed amount formulation, including an evaporant, on each depression or actuation of the dispensing structure.
In order for such a metering valve to discharge a formulation that includes a liquefied gas, the formulation must be maintained under pressure while it is being inserted into the bag within the container. The bag must therefore have a single port through which the contents thereof are both filled and discharged. That is, the bag in the container must be filled through the dispensing structure which extends into the bag. Although all metering valves release a predetermined volume of formulation on each actuation of the dispensing structure, such known valves do not permit filing of the formulation through a stem of the valve.
U.S. Pat. No. 3,104,785 to Beard discloses a metering valve that can be filled through the stem of the valve and discharges a fixed amount of formulation on each actuation of the dispensing apparatus. The '785 Beard device, however, inconveniently requires the dispensing stem to be in a depressed condition at the time the liquid formation is filled through the metering valve.
Thus, there a need and continuing desire for an improved metering valve that dispenses a volume of liquid formulation from a bag upon each actuation of the dispensing apparatus and which allows the bag in the container to be replenished from outside the container.